The incident took place Sunday in Oswiecim, the southern Polish town where Nazi Germany operated Auschwitz during World War II. It happened as Holocaust survivors gathered nearby to commemorate the anniversary of the camp’s liberation, a day also recognized each year as International Holocaust Remembrance Day.

Piotr Rybak, a far-right activist with a past conviction for burning the effigy of a Jew in 2015, could be seen in TV footage saying “we must tell Jewish invaders … that we are masters of this country.”

Mariusz Slomka, a deputy district prosecutor in Oswiecim, said Monday that prosecutors are investigating. In Poland, it’s a crime to incite hatred based on religion or race.